CS61A : THE STRUCTURE AND INTERPRETATION OF COMPUTER PROGRAMS
TIP SHEET ​
for ​
MIDTERM 1
1
TIPS FOR MIDTERM ​
Computer Science 61A . September 15, 2015 . ​
alvinwan.com/cs61a
This tip sheet does not comprehensively cover ​
all​
types of midterm questions. Instead, it
covers the three top types of problems.
01.​
ENVIRONMENT DIAGRAMS
See an outline of the steps at ​
http://sumukh.me/?/61a-enviroment-diag​
. It lists rules for all
tasks in an environment diagram. You should also draw environment diagrams for “Interactive
Output” questions on your midterm. Here is a recommended checklist to run through after
completing your diagram.
1. All frame names contain f<integer>: <intrinsic name>. In other words, check that all of
the intrinsic names are actually taken from the right side of your environment diagram.
They ​
are not​
the variables defined in a frame. They are the names of the function
defined on the right side.
2. Check that the parent of each function is where the function is defined, ​
not where it is
called​
.
3. Double-check that you do ​
not​
have frames for built-in or imported functions (you do
not know how these were implemented).
02.​
FILL IN THE BLANKS
Midterms feature fill-in-blank questions that cover topics such as recursion, iteration, and
lambdas. Note that these mold your approach to coding by encouraging you to understand
the most efficient and human-readable way to code.
CS61A FALL 2015 . written by Alvin Wan
go to ​
alvinwan.com/cs61a​
for more practice
CS61A : THE STRUCTURE AND INTERPRETATION OF COMPUTER PROGRAMS
TIP SHEET ​
for ​
MIDTERM 1
Lambda Functions
1. Convert into function form (complete function definitions using def, instead of
lambda)
2. If a blank is in the function parameters, check which variable is undefined in the body
of the function.
3. If a blank is in a function call, like f(______), determine what f is and then what to pass
to f.
Recursive Functions
1. Determine the types of each variable. (boolean, integer, float, string, None, or function)
2. Identify the three parts to any recursive function: base case, recursive case, and what
is being reduced with each function call.
3. According to what is given and if doctests are not provided, list expected output for
the program. Find a pattern, and use that solve the problem.
4. If it comes down to it, guess and check. Then, fix.
03.​
ADDITIONAL NOTES
Here are additional notes to remember or write down:
-
f1(f2(f3(5))))​
indeed evaluates ​
the inner function first​
. Therefore, you write the
innermost frame first. ​
Operands​
are evaluated before operators (arguments are
evaluated before the function), but the ​
call expression​
(actually calling expression)
occurs starting from the innermost function call. So, the first frame you write is f3.
-
Look up undefined variables in the function’s parent, which is strictly defined as the
frame in which it was defined.
CS61A FALL 2015 . written by Alvin Wan
go to ​
alvinwan.com/cs61a​
for more practice